1. Technical Field
The embodiments described herein are related to wireless communication and in particular to systems and methods for wireless indoor positioning.
2. Related Art
Wireless indoor positioning systems have become more popular in recent years. These systems are commonly used for asset tracking and inventory management. For example, these systems have been used for location detection of products in a warehouse, location detection of medical personnel or equipment in a hospital, location detection of firemen in a burning structure, and tracking of maintenance equipment scattered over a facility or compound.
Numerous wireless technologies have been developed or adapted for use in indoor positioning applications. These technologies include WLAN, RFID, UWB, ZigBee, Bluetooth, HomeRF, GPS, wireless assisted GPS, etc. In general, these technologies and systems based thereon tradeoff complexity and power requirements for range. In other words, the lower the power, the shorter the distance the over which the system will work effectively. FIG. 1 is a diagram taken from “Survey of Wireless Indoor Positioning Techniques and Systems,” H. Lui et al., IEEE Transactions on Systems, Man, and Cybernetics—Part C: Applications and Reviews, Vol. 37, No. 6, November 2007, which is incorporated herein by reference. The systems on the left tend to be low power systems, while the systems on the right are high power systems. As can be seen, the low power systems work over a relatively short range.
While many systems and techniques for wireless indoor positioning have been developed, there are still several deficiencies that limit adoption and deployment. Ideally, an indoor positioning system would comprise tracking devices that require very little power to operate so that the devices can be made very small, very inexpensively, and so that the devices can last longer on a single battery. The consumer of power within a tracking device is the transceiver. The further a device must transmit, the higher the transmit power required, which translates directly into higher power consumption within the device. As a result, very low power systems, such as UWB systems have been deployed. A UWB system can, for example, transmit effectively at transmit powers as low as −10 db.
But in order to be effective, such low power systems typically require very precise timing. This requires a high quality crystal oscillator to control the devices timing, which drives up cost, size, and power requirements. Thus, conventional systems cannot provide the extremely low power operation, and accuracy that is required for many applications.